Video data has come to be often delivered in real time as stream data, as the Internet and high speed communication services such as Asymmetric Digital Subscriber Line (ADSL) and Fiber To The Home (FTTH) infiltrate. However, it is not so easy to simultaneously deliver the stream data to a lot of clients. Normally, either a method of preparing a few large-scale servers or a method of preparing a lot of servers is adopted. However, they increase the cost of facilities or operations. In addition, it is necessary to process the video and voice in real time, and when a lot of clients are connected, it is very difficult to maintain the real-time delivery. For example, when a configuration where a lot of servers are connected to a lot of clients via a load distribution apparatus is adopted, the delay occurs at the load distribution apparatus anyway, and it is difficult to maintain the real-time delivery. Moreover, when a configuration where one server, for example, is connected with clients via a proxy, although the smooth video and voice can be delivered by the cache of the proxy to a lot of clients, the real-time delivery cannot be carried out by the cache. Furthermore, even if all the facilities are not used actually, the redundant design of the maximum configuration is required at the design. Therefore, when introducing the system, the tremendous cost is required. In addition, the expansion of the system is not easy.
In addition, for example, US-2001/042110-A1 discloses a technique to reduce the load of a parent server and/or a network connected to the parent server in a delivery system delivering contents to a plurality of clients, and to reduce the burden of an administrator and users of the delivery system by automatically switching delivery servers according to varying delivery requests. Specifically, in a delivery system having the parent server and a plurality of child servers and configured so that they can be connected with a plurality of clients via communication lines, the parent server selects a child server having contents requested to be delivered and being nearest the client of the delivery requesting source based on received position information of the client and identification information of the contents to notify the client of the delivery requesting source. Then, the selected child server responds to the request of the client of the delivery requesting source and delivers the contents requested to be delivered. However, the child servers are provided fixedly, and when clients whose number exceeds the permissible number requests the delivery, the expansion of the child servers is needed.